Use of correlation combination to achieve channel detection
View Patent ↗Combinations of correlation results are used to achieve detection of multiple coded signals at a receiver in a wireless communications system. The code applied to signals includes a lower rate code and a higher rate code. The lower rate code is a nested or tiered code such that it comprises at least two code sequences of the higher rate code. The received coded signal is correlated with the higher rate code using a single higher rate correlator to provide a higher rate code correlation result. The higher rate code correlation results are fed to two or more lower rate code correlators that combine multiple higher rate code correlation results, each using a different lower rate code, to provide corresponding lower rate code correlation results. The presence of at least one coded signal or mutually exclusive coded signals can be determined from the lower rate code correlation results.
1. A method of detecting a received coded signal in a receiver wherein the code applied to the received coded signal includes a lower rate code comprising at least two code sequences of a higher rate code, the method comprising:
correlating the received coded signal at the receiver with the higher rate code to provide a higher rate code correlation result;
correlating the higher rate code correlation results with a first lower rate code to provide a first lower rate code correlation result;
correlating the higher rate code correlation results with a second lower rate code to provide a second lower rate code correlation result; and
comparing the first lower rate code correlation result to the second lower rate code correlation result to determine the presence of a signal indication.
2. The method of claim 1 , further comprising determining the presence of a first indication corresponding to the first lower rate code from the first lower rate code correlation result.
3. The method of claim 1 further comprising determining the presence of a second indication corresponding to the second lower rate code form the second lower rate code correlation result.
4. The method of claim 1 further comprising determining the presence of one or another of two mutually exclusive signal indications form the first and second lower rate code correlation results.
5. The method of claim 1 wherein the received coded signal is received periodically.
6. The method of claim 1 wherein the lower rate codes are orthogonal to each other.
7. The method of claim 1 wherein the lower rate codes are Walsh codes.
8. The method of claim 1 wherein the lower rate codes are Gutleber codes.
9. The method of claim 1 wherein the lower rate codes are maximum length sequences.
10. The method of claim 1 wherein the lower rate codes are PN-sequences.
11. The method of claim 1 wherein the higher rate code is 32 chips in length and the lower rate codes are 128 chips in length.
12. The method of claim 1 wherein the lower rate codes are used for timing signals.
13. A method of detecting a received coded signal in a receiver wherein a code applied to the received coded signal includes a lower rate code comprising at least two code sequences of a higher rate code, the method comprising:
demodulating the received coded signal at the receiver into in-phase and quadrature components;
correlating the in-phase and quadrature components with the higher rate code to provide higher rate code correlation results;
correlating higher rate code correlation results with a first lower rate code to provide a first lower rate code correlation result;
correlating higher rate code correlation results with a second lower rate code to provide a second lower rate code correlation result; and
comparing the first lower rate correlation result to the second lower rate code correlation result to determine the presence of a signal indication.
14. The method of claim 13 wherein the lower rate codes belong to a set of M possible lower rate codes, and the steps of correlating the higher rate code correlation results are based on N of the set of M lower rate codes to provide N lower rate code correlation results where N is less than M.
15. The method of claim 14 further comprising determining the presence of at least signal indication from the N lower rate code correlation results.
16. The method of claim 14 further comprising determining the presence of mutually exclusive signal indications from the N lower rate code correlation results.
17. The method of claim 14 further comprising determining the presence of N mutually exclusive signal indications from the N lower rate code correlation results.
18. The method of claim 14 further comprising determining the presence of a subset of N mutually exclusive signal indications from the N lower rate code correlation results.
19. The method of claim 14 wherein the N lower rate codes are selected based on a priori system information.
20. The method of claim 14 wherein the received coded signal is received periodically.
21. The method of claim 14 wherein the lower rate codes are orthogonal to each other.
22. The method of claim 14 wherein the lower rate codes are Walsh codes.
23. The method of claim 14 wherein the lower rate codes are Gutleber codes.
24. The method of claim 14 wherein the lower rate codes are maximum length sequences.
25. The method of claim 14 wherein the lower rate codes are PN-sequences.
26. The method as in claim 13 wherein the lower codes are nested codes comprising at least two code sequences of a base code and N nested lower rate codes are selected from of a set of M possible nested codes.
27. The method of claim 26 further comprising determining the presence of mutually exclusive signal indications from the N lower rate code correlation results.
28. The method of claim 26 further comprising determining the presence of N mutually exclusive signal indications from the N lower rate code correlation results.
29. The method of claim 26 further comprising determining the presence of a subset of N mutually exclusive signal indications from the N lower rate code correlations results.
30. The method of claim 26 wherein the N nested codes are selected based on a priori system information.
31. The method of claim 26 wherein the received coded signal is received periodically.
32. The method of claim 26 wherein the nested codes are orthogonal to each other.
33. The method of claim 26 wherein the nested codes are Walsh codes.
34. The method of claim 26 wherein the nested codes are Gutleber codes.
35. The method of claim 26 wherein the nested codes are maximum length sequences.
36. The method of claim 26 wherein the nested codes are PN-sequences.
37. The method according to claim 13 further comprising using a higher rate code correlator with the higher rate code to correlate the in-phase and quadrature components with the higher rate code to provide higher rate code correlator output; and
sharing the higher rate code correlation output to feed two or more lower rate code correlators that each use a different one of the lower rate codes to provide the first and second lower rate code correlation results.
38. The method of claim 37 wherein N lower rate codes are selected from a set of M possible codes and the N lower rate codes are selected based on a priori system information.